Locks

ABSTRACT

This device is a bolt type lock for preventing tampering with gas and electric meters. A hollow body with a fixed head on one end has a cap held onto the other end by locking means held extended into the cap by a spring-loaded plunger retractible solely through a small round key hole in the head, to unlock the lock. If any tool but the authorised key is used to pull the plunger, a piece that is normally left behind when the genuine key is used is brought into position in place of the plunger and keeps the locking means extended and the lock locked.

United States Patent 11 1 1111 3,835,674 Hoyt 1451 Sept. 17, 1974 [54]LOCKS FOREIGN PATENTS OR APPLICATIONS [75] Inventor: Richard HoytWorcester, Mass- 1,354,923 2/l964 France 339/91 B [73] Assignee: OMCOlnc., Holden, Mass. [2 ed Ap 20 1973 Primary Exammer-Robert L. Wolfe 211App]. No.: 352,983 [57] ABSTRACT This device isa bolt type lock forpreventing tamperl. mg with gas and electric meters- A hollow body witha g Eosb fixed head on one end has a cap held onto the other [58] Fieid"5 32 33 end by locking means held extended into the cap by aspring-loaded plunger retractible solely through a 70/25 292/252 339/91B small round key hole in the head, to unlock the lock. [56] ReferencesCited If any tool but the authorised key is used to pull the UNITEDSTATES PATENTS plunger, 21 piece that is normally left behind when thegenuine key is used is brought into position in place of wolrse v theplunger and keeps the locking means extended I gus 3,186,196 6/1965Moberg.. and the lock locked 3,714,802 2/1973 Morse 70 34 9 Claims, 4Drawing Figures LOCKS This invention is an improvement in plunger typelocks, such as are used on shut-off valves or switches, designed to makeit practically impossible to open the lock without the proper key.

Plunger type locks of the construction shown in U.S. Pat. Nos. 1,923,025and 3,714,802 to L. H. Morse et a1. and 3,002,368 to Moberg are sowidely employed by gas and electric public utility companies to preventunauthorized opening of gas supply valves and tampering with electricitymeters that efforts to pick these locks are sometimes successful on thestrength of knowledge or deduction of the manner of operation of thelock.

The only effective point of attack is through the extremely narrowcircular aperture at one end which forms the keyhole. By thinning theend of a common nail to spade shape and distorting it by hammering itinto the socket in the plunger it is occasionally possible to obtain thefrictional engagement with the walls of the socket needed to retract theplunger against the resistance of its spring and thus release thelocking balls and open the lock.

The present invention defeats this method of lockpicking by making theplunger in two parts, such that the jamming of the nail end in theplunger socket wedges the two parts together to move in unison andobstruct the inward unlocking migration of the locking balls; but whenthe authentic key is used the two parts separate and let the balls moveinward to unlock the plunger.

An illustrative embodiment is shown in the drawings, in which FIG. 1 isan axial section of the lock in locked relation.

FIG. 2 is a similar view of the parts shown in FIG. 1 in unlockedrelation.

FIG. 3 is a transverse section on line 3-3 of FIG 1.

FIG. 4 is a transverse section on line 4 4 of FIG. 2.

Having reference to the drawings, the lock comprises a tubular body orbolt 1 and a plunger 3 slidable therein and pressed toward the closedend of body 1 by spring 5. One end 7 of plunger 3 is of reduceddiameter, an annular shoulder 9 thereof abutting against an internalannular shoulder 11 formed by reducing the bore of body 1 at 8 to fitthe end-portion 7, the engagement of these shoulders limiting the extentof movement of plunger 3 as biased by spring 5. In this relation, theendportion 7 holds two steel balls 13 partly extended radially of theplunger from the opposite ends of a bore 15 formed diametrically throughthe walls of the counterbore 8, and having inwardly swaged ends. Thusextended, these locking members 13 are received in one of annulargrooves 17 formed inside a cap 19 fitting freely over the end of body 1,locking the cap removably in place thereon.

The other end of body 1 is closed by a cap 21 pressfitted or otherwisepermanently fixed thereon, and having an axial bore 23 forming thekeyhold of the lock, as will appear.

In use, the device is employed as a locking bolt, as by putting the bodyportion 1 through aligned apertures in the fixed arm 25 and movablevalve-operating arm 27 of a valve in a pipeline, for example, and thenapplying the cap 19 to lock the valve in closed relation. The

plunger 3 is drawn back by a key such as that of Moberg U.S. Pat. No.3,033,016 until portion 7 lets the balls 13 recede within the surface ofbody 1 as shown in FIG. 2, permitting cap 19 to be applied to the end ofbody 1 as shown in FIG. 1. Removal of the key releases the plunger toreturn under the push of spring 5, extending the balls 13 into one ofthe grooves 17 and locking the cap in place.

In accordance with the invention, as already indicated the ball-engagingportion of plunger 3 is made in two parts. The reduced inner end 7 ofthe plunger which holds the locking balls 13 extended is formed with acylindrical axial bore 29, in which is slidably mounted a pin 31 havinga cylindrical head 33 of the same diameter as the ball-engaging endportion 7 of the plunger 3. The shank of the pin 31 terminates ina'conical point 35 of 30 taper. When the pin is in inmost position inthe cylindrical portion of bore 29 the base portion of the cone is atthe narrow end of a conical enlargement 37 of 30 taper in the bore 29.The remainder 39 of the bore is cylindrical.

The dimensions of the parts and of the spring 5 when fully compressedare such that if the pin 31 holds its position in bore 29 as plunger 3is fully retracted, the head 33 of the pin 31 will be brought into aposition between the balls 13 and will hold them extended as shown inFIG. 3, thus keeping the lock locked, so if a nail or other lock-pickingmeans driven into the cavity 37, 39 of the plunger manages by remotechance to wedge tightly enough to be able to retract the plunger againstthe thrust of spring 5 it will do so by wedging against the slope of thecone 35 of the pin 31 and accordingly hold the pin from relativemovement in the plunger. Thus the head 33 will follow the portion 7 intoposition between the balls 13 and the lock will stay locked.

However, when the authentic key capable of exerting the necessary radialfrictional gripping power against the wall of cylindrical portion 39 tolet the user over power spring 5 and move the plunger clear of the balls13, the pin 31 is left behind as shown in FIG. 2 and only its shank isbetween the balls 13, which differential movement as shown in FIG. 4lets the balls move inward out of engagement with the groove in cap 19,releasing the cap and thus effecting the unlocking of the lock.

The head 33 is made a close fit in the bore 29 so that, piston-like, theair pressure applies a slight restraint to hold it from following theretreating end of portion 7 of the plunger. Additionally, a film of oilsealing the head to the bottom and sides of bore 29 can be used to helpovercome machining deficiencies.

With the included angle of between the slope of the conical end 35 ofthe pin 31 and the conical wall 37 it is practically impossible for theflattened end of a driven nail to recurve into jamming relation with thepin or the wall 39 tightly enough to pull the plunger far enough tounlock the cap 19.

Thus made according to the invention the lock is' practically incapableof being picked.

While I have illustrated and described certain forms in which theinvention may be embodied, I am aware that many modifications may bemade therein by any person skilled in the art, without departing fromthe scope of the invention as expressed in the claims. Therefore, I donot wish to be limited to the particular fomis shown, or to the detailsof construction thereof, but

What I do claim as my invention is:

1. A lock having a tubular body, radially extendible locking membersthereon, a spring-biased. plunger therein actuating such members andretractable clear of the locking members, and means within the bodyadapted to hold the locking members extended when the plunger iswithdrawn from actuating relation with such members by wedging meansengaging both the plunger and the said means.

2. A lock according to claim 1 in which the said means alternativelyholds and releases the locking members.

3. A lock according to claim 1 in which the said means moves withtheplunger to hold the locking members in locking relation and movesrelatively to the plunger to release the locking members.

4. A lock according to claim 3 in which the said means remains at restwith respect to the plunger to release the locking members.

5. A lock according to claim 1 in which the plunger has an axial boreand the said means is relatively movable in such bore.

6. A lock according to claim 5 in which the said means holds the lockingmembers extended when it and the plunger move in unison.

7. A lock according to claim 5 in which the said means is relativelymovable with respect to the plunger and ceases to hold the lockingmembers extended upon independent movement of the plunger with respectto such means.

8. A lock according to claim 1 in which the plunger has an axial boreand the said means has a shank slidable in such bore and a headextending beyond the bore engaging the locking members when the plungeris withdrawn from actuating relation with such members.

9. A lock according to claim 8 in which differential movement betweenthe plunger and the shank keeps the head out of engagement with thelocking members.

1. A lock having a tubular body, radially extendible locking membersthereon, a spring-biased plunger therein actuating such members andretractable clear of the locking members, and means within the bodyadapted to hold the locking members extended when the plunger iswithdrawn from actuating relation with suCh members by wedging meansengaging both the plunger and the said means.
 2. A lock according toclaim 1 in which the said means alternatively holds and releases thelocking members.
 3. A lock according to claim 1 in which the said meansmoves with the plunger to hold the locking members in locking relationand moves relatively to the plunger to release the locking members.
 4. Alock according to claim 3 in which the said means remains at rest withrespect to the plunger to release the locking members.
 5. A lockaccording to claim 1 in which the plunger has an axial bore and the saidmeans is relatively movable in such bore.
 6. A lock according to claim 5in which the said means holds the locking members extended when it andthe plunger move in unison.
 7. A lock according to claim 5 in which thesaid means is relatively movable with respect to the plunger and ceasesto hold the locking members extended upon independent movement of theplunger with respect to such means.
 8. A lock according to claim 1 inwhich the plunger has an axial bore and the said means has a shankslidable in such bore and a head extending beyond the bore engaging thelocking members when the plunger is withdrawn from actuating relationwith such members.
 9. A lock according to claim 8 in which differentialmovement between the plunger and the shank keeps the head out ofengagement with the locking members.